Man and the industrialized world has continually wrought havoc on the natural environment and the public is consistently reminded of the undesirable side effects of the unfettered discharge of industrial wastes and other forms of air, water and soil pollutants. While it is still unclear exactly how much irreparable damage has been done up to this point in time, it is evident that positive steps must be taken to reverse the direction in which today's society is going and every effort must be made to save and rehabilitate that which has been already damaged.
Soil pollution is a major problem which must be addressed in the very near future. Unbridled and thoughtlessly uncontrolled dumpings of solid, liquid and gaseous pollutants find their way into the soil and can remain there for years. Polycyclic hydrocarbons, a common class of chemicals discharged by industries everywhere, possess toxic, mutagenic and carcinogenic properties. Hydrocarbon solvents have been carelessly dumped into the soil for years and problematically remain there with nowhere else to go. Thousands of tons of toxic compounds are buried in the soil every year in huge commercial landfills and these are scattered throughout the surrounding area for miles by rain and sub-surface ground water. Besides industrial and municipal wastes, pesticides, herbicides, and insecticides ultimately end up in the soil and, as they are not readily degradable, persist there for a long time.
Soil pollutants widely prevalent today are known as volatile organic contaminants which are organic compounds such as low molecular weight alkanes, alcohols, amines, amides, acids, sulfites, dioxins, ethylbenzenes and PCBs. Soil decontamination of these compounds as well as other pollutants has been achieved to a limited extent through solvent extraction, coagulation, high pressure cleaning, supercritical fluid extraction, thermal desorptions, soil vapor extraction, incineration and microbial oxidation. Physical means include pumping the ground soil with water followed by air stripping the soil to remove the volatile hydrocarbons, vacuum extraction and site excavation followed by incineration of the contaminated soil.
U.S. Pat. No. 4,738,206 to Noland discloses a process and apparatus for the low temperature thermal stripping of volatile organic contaminants from the soil. The contaminated soil is heated under negative pressure and is passed through a hollow screw conveyor with hot oil. The soil/oil composition generates combustion gases containing the volatile organic compounds which are removed from the system using a temperature gradient.
U.S. Pat. No. 4,702,178 to Welsh teaches an emergency exhaust system for an industrial hazardous waste incinerator including means for the conveyance of contaminated wastes under a series of rakes and infrared heating elements whereby the solid toxic waste materials are oxidized through the application of intense heat to combustion gases which are drawn off and removed.
U.S. Pat. Nos. 4,993,943 and15,178,077 to Norris discloses a screw conveyor apparatus and soil purification process in which volatile organic contaminants are removed from the soil by guiding and agitating the soil with the screw conveyor while at the same time heating the soil with infrared radiation which volatizes the organic contaminants which are then driven off by venting the chamber with an oxidizing, reducing or inert gas.
U.S. Pat. No. 5,425,881 to Szejtli, et al. discloses a method for the extraction of organic pollutants from contaminated soils comprised of mixing the contaminated soil with an aqueous solution of cyclodextrins and their derivatives. The cyclodextrins and their derivatives allegedly desorb the toxic organic compounds from the soil and keep them in a solubilized form which is based on the formation of an inclusion complex by the molecules. The soil is then inoculated with a bacteria or fungal culture capable of biodegrading the organic pollutants. The solubilized inclusion complex makes the organic contaminants more susceptible to this biodegradation.
Finally, Szejtli; et al. also describes another attempt at the enhancement of pollutant biodegradation in the soil by increasing the bioavailability of the organic contaminants through desorption of the soil. Desorption is carried out by chemically treating it with a hydroxylating reagent (H.sub.2 O.sub.2 --Fe.sup.2), a surface active agent or other solvent.
None of these prior art methods efficiently and cost-effectively remove highly volatile organic contaminants from the soil so as to purify it to its natural state without left-over solvent or combustion residues. Nor does any of the prior art provide a simplistic, cost effective method that can be used to clean large scale pollution problems rendering the otherwise toxic soil suitable for agricultural and livestock applications.